Usually the definitions of two important quality factors – homogeneity and uniformity – are easily mixed up in a deposition process no matter which coating technologies are involved. Note that many articles, papers or technical notes made the same confusion. So, the definitions must be clear.
Homogeneity generally considers a very local spot area and measure/check the layer properties along the direction of the layer grown.
Uniformity considers the differences or tolerances among several measured data along one axis or in a big XY-plane area.
PEM system normally takes the responsibility of layer’s homogeneity control.
Uniformity can be achieved if the process chamber has a good layout or configuration for reactive plasma process.
To achieve a good homogeneity layer, PEM system was introduced to reactive plasma processês to ensure the composition fraction (or alloy fraction) in each compound or molecules formed by the reactive plasma process is nearly constant.
Uniformity is a very important factor to be concerned and it’s very complicated because there are many factors that can influence it. Generally, process chamber’s configuration is most critical to get a good uniformity of the grown layer.
This example has 3 measuring points over the width 1300mm of the PET film to compare the thickness, refractive index and other data corresponding to the uniformity in 3 locations in the same XY-plane on the surface of PET film.
The factors often influencing the uniformity include: